1. Field of the Invention
The present invention relates to a communication apparatus, and more particularly to a communication apparatus for measuring a communication time.
2. Related Background Art
A facsimile machine which has a function to measure a communication time of the facsimile machine and calculate a charge based thereon and display it or print it out on a record sheet, has been known. In order for such an apparatus to calculate the exact charge, it is necessary to measure exactly the line capture time.
In the prior art facsimile machine, it is usual to measure the time during which the facsimile machine captures the line. In such an apparatus, if an operator leaves the handset of a telephone set connected to the facsimile machine off the hook when the communication is terminated, the line is kept captured by the telephone set even if the line is switched from the modem to the telephone set, and the charge continues to accrue. Nevertheless, the facsimile machine calculates the charge based on the time to the termination of communication. As a result, the actual charge for the use of the line does not coincide with the charge indicated by the facsimile machine.
It has been proposed to provide a detector to detect whether the line is captured or not so that the time is measured if the off-hook state is detected at the end of communication and the time and charge are calculated and displayed when the line is released.
In this method, however, when the line is captured while the telephone set is in the off-hook state after the termination of communication, a control unit is in operation only for measuring the time, and power is wasted.
Further, in this method, if the control unit is busy, for example, in a copy operation when the telephone set is finally hung up, the release of the line is detected only after the busy status has been released or terminated. As a result, the exact line capture time cannot be measured.
U.S. patent application Ser. Nos. 915,430, filed on Oct. 6, 1986, and 009,528, filed on Feb. 2, 1987, both assigned to the assignee of the present invention, display prediction of communication end time or communication charge.